London, Nov 07 - United States President Barack Obama has reportedly sent a "secret letter" to Iran's Supreme Leader Ayatollah Ali Khamenei describing a shared interest in combating the Islamic State ( IS).

According to the BBC, Obama stressed that any co-operation in taking on the terror group is dependent on Iran reaching a nuclear agreement by November 24 diplomatic deadline.

The letter was sent last month and is at least the fourth letter written by Obama to Khamenei after he assumed office in 2009.

U.S. Secretary of State John Kerry is scheduled to begin negotiations on the issue with Iranian counterpart Javad Zarif this weekend in Oman.

The White House has declined to comment on the private correspondence. (ANI)